Such a method is known from EP 2 266 782 A1, wherein the therein disclosed device delivers solidifiable material plasticized with a plasticising unit known in injection molding technology in a fluid phase into a material storage. The material storage is pressurized and this pressure is used to discharge the material in the form of drops via a clockable discharge opening in order to produce a three-dimensional object in a construction chamber. The fluid phase of the material comprises a temperature dependent viscosity. A solid body joint is used for discharging the drops at the discharge opening, the pretension of which can be regulated. For this purpose the operation point of the solid body joint is measured and readjusted, if necessary. Specific displacement/force curves can be driven with an actuating element actuating the solid body joint, in order to targetedly and consciously influence the form of the drops.
Such a method is also known from DE 10 2004 025 374 A1, in which drops of one reaction component are discharged and brought into contact with a basis reaction component present on a substrate, in order to produce a three-dimensional object with varying material characteristics layer by layer. This causes a gradual transition from one material characteristic to another material characteristic. The drop size can be regulated in dependency of a measured layer thickness without having attention to the viscosity of the processed material which viscosity may eventually change during the production process.
EP 1 886 793 B1, in which a plasticising unit known in injection molding technology is coupled to a pressurized material storage means to produce a fluid phase of a material. To produce an object on an object support in a construction chamber, this material is discharged via a discharge opening in the form of drops, it being necessary to apply a high pressure and generally also high temperatures due to the adhesive strength of the material.
In this device the advantages of plastics parts production using standard materials used conventionally in injection molding is combined with the possibility of producing plastics parts for single-item or small batch production. It allows parts to be produced without a mold which parts have properties similar to those of injection-molded parts.
To produce such individual parts or small batch sizes, such as for example samples, further manufacturing processes are also known, which are known widely as “prototyping” and “rapid manufacturing”. Such parts are produced without using molds, the geometry in most cases being produced on the basis of 3D data. These geometries are produced in a wide variety of forms using appropriate means such as melting powder layers by the application of heat, for example by means of a laser, additive systems such as printing processes, the powder particles being bound in different ways, or also using so called melt strand methods.
In practice it has been found that when using the method known from EP 1 886 793 A1 for production purposes, a relatively long construction time is needed for one part. Although as little melt as possible is kept in the melt pressure generator and thus in the entire system through the geometric construction, on the other hand this amount must not be too little, since otherwise every opening of the outlet opening on the discharge of the drops has a significant dynamic effect on the pressure level, which the melt pressure controller cannot track due to the inertia thereof. On the other hand, the amount of plastics discharged is dependent on the following parameters: temperature, the liquefied melt in the pressure generator, melt pressure and outlet nozzle geometry and also opening times and stroke of the orifice plate of the outlet opening and also the viscosity of the molten material influenced by the total residence time. In addition, the intrinsic viscosity of the plastics material reduces viscosity at higher shear rates, which in turn affects drop size and their tendency to coalesce with drops which already previously have been discharged.
The prior art also discloses a measurement method in which material discharge per unit time from the nozzle is determined. The value is stated in g/10 min, the plastics material being forced through a nozzle with a diameter of 2.095 mm by means of a plunger. The necessary force is applied by a weight. When stating the values the test temperature and nominal mass used must always be stated. The method is defined according to DIN EN ISO 1133. When determining the MFI value, which corresponds to the melt flow rate, established in this way, the fluidity of the plastics material is determined only at a defined operating point. Any change in fluidity as process parameters change, in particular as a function of residence time, is not taken into account.